Stoma caps or covers, which are used with a colostomy stoma, have been provided with gas-venting filters. See, for example, U.S. Pat. No. 3,804,091. Such caps fit snugly over the stoma, and are not designed to receive large amounts of discharge. They are essentially protective covers, and usually include an absorbent pad for collecting a small amount of discharge. In accordance with prior design, as described in the cited patent, the gas is vented through the filter by a circuitous route to provide greater contact between the activated carbon of the filter and the vented gas. The resulting restriction in the rate of gas venting may cause a pressure build-up resulting in discomfort to the wearer, who may have to correct the condition by temporarily breaking the seal between the cap and the skin area surrounding the stoma.
It has been proposed to provide certain other kinds of collection devices, such as colostomy pouches, with gas-venting filters. Prior art devices of this type are described in U.S. Pat. Nos. 3,952,727 and 3,759,260. The filters of both of these patents also utilize an indirect or circuitous gas venting principle. This is accomplished, for example, by forcing the gas to enter the end of the filter cake, or by offsetting openings in the inner and outer covers of the filter cake. Colostomy devices equipped with such filter assemblies could therefore permit a build-up of pressure to occur within the pouch under conditions where large amounts of gas are being discharged from the stoma. This would cause the pouch to distend or "balloon". This is objectionable to the wearer because it makes the ostomy appliance more noticeable. Such "ballooning" of colostomy pouches is a recognized problem for the wearers of stoma pouches. To prevent such distension of the pouch, ostomates have resorted to expedients, such as making pinholes in the pouch, or temporarily breaking the seal of the pouch to the skin, thereby "burping" the pouch. Either practice is objectionable because of the release of unpleasant odors.
As will be apparent from the foregoing discussion, there has been a need for a gas-venting filter assembly which can be applied to collection appliances to preclude gas build-up and ballooning of the appliance while deodorizing the vented gas. With such a free venting filter, however, there may be a problem in the transmission of liquid from within the pouch. There is also a problem of protecting the filter assembly from external water if the appliance is worn while the ostomate is taking a shower.
Still another design problem is that the collection appliance should be capable of being tested for leakage during manufacture. The wearer needs assurance by such testing that the pouch is fully sealed and has no leaks through which liquid or gas can escape. The leakage testing has ordinarily been carried out by inflating the pouch, but where the pouch contains a free venting filter this is difficult to carry out.